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Polyatomic molecules with emission quantum yidld >20% enable efficient organic light-emitting diodes in the NIR(II) window
S.-F. Wang, B.-K. Su, X.-Q. Wang, Y.-C. Wei, K.-H. Kuo, C.-H. Wang, S.-H. Liu, L.-S. Liao,* W.-Y. Hung, L.-W. Fu, W.-T. Chuang, M. Qin, X. Lu, C. You, Y. Chi,* P.-T. Chou*
The emission of light by polyatomic molecules in the spectral region of the second near-infrared (NIR(II)) window is severely hampered by the energy gap law, namely the quenching induced by exciton–vibration coupling. As a result, organic light-emitting diodes (OLEDs) with efficient emission wavelengths of ~1,000 nm and above are rare, despite their potential for phototherapy and bioimaging. In this study we revisit the theory of the energy gap law to quantify the contribution of each coupled vibrational mode to non-radiative transitions. The results lead us to propose two approaches that favour emission: molecular packing to extend exciton delocalization, and deuterium substitution to reduce high-frequency vibrations. We provide an experimental proof of concept by designing and synthesizing a new series of self-assembled Pt(II) complexes that exhibit high-intensity phosphorescence with peak quantum yields of (23 ± 0.3)% at approximately 1,000 nm. The corresponding OLEDs emit at a peak wavelength of 995 nm with a maximum external quantum efficiency of 4.31% and a radiance of 1.55 W sr−1 m−2, marking a substantial contribution to the development of efficient OLEDs in the NIR(II) region.